1. Field of the Invention
The present invention relates to a monolithic capacitor which is employed as a temperature-compensating capacitor, and to a process for producing the capacitor; and more particularly to a monolithic capacitor in which a base metal is employed as an internal electrode material, and to a process for producing the capacitor.
2. Background Art
Conventionally, a monolithic capacitor in which an Ni internal electrode is formed inside a sintered ceramic body predominantly comprising CaZrO3xe2x80x94CaTiO3 is known as a temperature-compensating capacitor. In order to produce the monolithic capacitor, firstly, a ceramic slurry is prepared through the following processes:
(1) CaCO3, ZrO2 and TiO2 are calcined in advance and pulverized to thereby obtain calcined powder, a sintering aid is added to the resultant powder, and an organic binder is added to the resultant mixture and the mixture is kneaded, to thereby prepare a ceramic slurry; or
(2) pre-calcined CaZrO3 powder and CaTiO3 powder are mixed with a sintering aid, and an organic binder is further added to the resultant mixture and the mixture is kneaded, to thereby prepare a ceramic slurry.
The thus-prepared ceramic slurry is shaped into a ceramic green sheet. Subsequently, an internal electrode is printed on the ceramic green sheet and a plurality of the resultant ceramic green sheets are laminated with one another. Then, onto each of the outermost ceramic green sheets, a ceramic green sheet on which the internal electrode is not printed is laminated, thereby producing a laminate. Thereafter, the laminate is fired to thereby produce the aforementioned sintered ceramic body.
However, in the CaZrO3xe2x80x94CaTiO3 monolithic capacitor produced through the above-described conventional process, the sintered ceramic body does not have a completely uniform structure i.e., a secondary phase may be generated in the ceramic body.
Particularly, when a ceramic slurry is prepared through the aforementioned process (2), a considerable amount of the secondary phase is generated in the resultant sintered ceramic body.
In the case in which the ceramic layer between the internal electrodes is thin, when the secondary phase is generated, a component contained in the phase tends to lower the reliability of the monolithic capacitor.
Therefore, maintaining the reliability of the CaZrO3xe2x80x94CaTiO3 monolithic capacitor is difficult, particularly when the thickness of the sintered ceramic layer between the internal electrodes is as thin as 5 xcexcm or less.
In view of the foregoing, an object of the present invention is to provide a monolithic capacitor comprising a sintered body formed from a TiO2-containing reduction-resistant dielectric ceramic material, and a process for producing the capacitor. The reliability of the monolithic capacitor can be maintained even when the sintered body of the capacitor has a non-uniform structure, i.e., when the secondary phase is generated in the sintered body in addition to the primary crystal phase, and when the sintered ceramic layer between internal electrodes is thin.
Accordingly, in a first aspect of the present invention, there is provided a monolithic capacitor comprising a sintered body formed from a TiO2-containing reduction-resistant dielectric ceramic material; a plurality of internal electrodes which are formed inside the sintered body, the electrodes being formed of a base metal; and first and second external electrodes which are formed on the sintered body, the internal electrodes being electrically connected to the external electrodes; wherein the amount of Ti contained in a secondary phase of the sintered body is about 2 wt. % or less as reduced to TiO2.
Preferably, the TiO2-containing reduction-resistant dielectric ceramic material predominantly comprises CaZrO3 and CaTiO3.
In a second aspect of the present invention, there is provided a process for producing a monolithic capacitor comprising a sintered body formed from a TiO2-containing reduction-resistant dielectric ceramic material and a plurality of internal electrodes which are formed inside the sintered body, the electrodes being formed of a base metal, which process comprises providing a laminate predominantly formed from the TiO2-containing reduction-resistant dielectric ceramic material, the laminate comprising a plurality of the internal electrodes formed of a base metal; firing the laminate at a temperature-elevation rate of about 5xc2x0 C./minute or more, to thereby obtain a sintered ceramic body in which the amount of Ti contained in a secondary phase of the sintered ceramic body is about 2 wt. % or less calculated as TiO2; and forming first and second external electrodes on the sintered ceramic body, the internal electrodes being electrically connected to the external electrodes.
Preferably, the TiO2-containing reduction-resistant dielectric ceramic material predominantly comprises CaZrO3 and CaTiO3.